Huge instability and insanely large memory footprint in 9.04

[Evan]

On Fri, Sep 25, 2009 at 7:40 AM, Marius Gedminas <marius at pov.lt> wrote:

> On Fri, Sep 18, 2009 at 04:46:21AM -0700, J. Lennard wrote:
> > First I'm sorry to write what may appear as a rant, but I hope it is
> > not considered so. I'm writing to express huge instability problems in
> > Ubuntu 9.04. I migrated from ubuntu 8.04 (386) to ubuntu 9.04 (amd64)
> > using a simple clean install.
> ...
> > I don't really know where to start. During past month, my machine
> > constantly went to trashing mode where the hard-disk light is
> > constantly on and I can't access anything or even swtich to linux
> > console for several *minutes*. This has occured more than four times
> > although all I usually run is a pdf viewer, an mp3 player, emacs, and
> > firefox with simple html pages (not even gmail, flash, etc).
>
> Do you have any swap space?
>
> I've got an Asus EeePC 900 with 1 GB of RAM.  Twice now I've experienced
> the same thing: constant disk I/O, huge latencies for any desktop task
> (switching windows, launching terminals).  I suspect a bug in the Linux
> VM subsystem, since *I was not running out of memory*.  Usually about
> 40-50% of my RAM is in disk cache---I keep track of memory usage via a
> GNOME panel applet.  On those occasions cache size was shrinking,
> completely free memory was increasing, all application pages were being
> constantly swapped out and back in causing constant disk I/O (which is
> painful on an SSD).  The fix was to create a temporary swap file in
> /tmp:
>
>  sudo -s
>  dd if=/dev/zero of=/tmp/swapfile bs=1M count=1024
>  mkswap /tmp/swapfile
>  swapon /tmp/swapfile
>
> Instantly the system became responsible again, after using ~400
> *kilobytes* of swap.
>
> I can only assume that having 0 swap space confused the VM somehow and
> kicked it into a full-on panic "let's free all the ram we can" mode.
>
> This swap file disappears after a reboot, and so far the problem hasn't
> recurred, so I didn't bother setting up a permanent swap partition (I'm
> afraid to destroy my SSD too quickly with constant writes---this already
> happened once thanks to ext3's journal).
>

I have had this occur several times to me on a quad-core with 3GB ram (and
6GB swap), but only ever when resuming. If I suspend with all free memory
used by cache (according to the Gnome panel applet), then occasionally on
resume it spends ~5minutes unresponsive with massive disk IO before coming
up. When it does come back everything is fine, except that all of that space
which was cache is now completely empty. I set my vm.swappiness value to 0
(because I so rarely need it), so while I'm definitely not running out of
swap space, I can see how swappiness=0 might cause the same sort of effect.
I haven't found anything odd in the logs so I never filed a bug, but if it's
happening to other people in other situations this bears investigating. I
will open a bug on this as soon as I have time.
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